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Abstract

"Paleozoic succession in Libya offers much potential for scientific investigation and oil industry exploration due to the prolific reserve of hydrocarbons contained within the rocks of that region. The Paleozoic stratigraphy in Libya is divided into two mega sequences, a lower sequence extending from Cambrian to Silurian and upper sequence extending from Devonian to Permian. Mamuniyat Formation, a late Ordovician outcrop succession which is the main reservoir in Murzuk Basin, is composed of massive cross-bedded sandstone, most of which is generally medium to coarse grain. In B-NC115 field, the Mamuniyat Formation shows varied thickness which is a result of paleotopographic highs of glacial related origin. This formation is divided into three sequences based on the lithofacies and well log data pattern. The upper sequence, which was deposited when sea level fell, is the producing unit that has more than 100 ft (30.40 m) of net pay in some areas with good porosity and permeability. This sequence has three facies, and has thickness of 200 ft (60.96 m) of sand, interbeded with shales. They range from one foot to several feet and are recognized by log pattern and also field observation. Depth, structure, and isochron maps addressed the paleohigh structure, which is a combination of structure and stratigraphic feature. The reservoir shows good porosity and permeability range from 9% to 12%, and 500-1000 mD respectively. Seismic interpretation showed the progressive onlapping of the Silurian shale units over the Mamuniyat paleohighs, which known as the paleoglacial related trap. Although there is no significant fault signature in the field, a possible normal-faulted anticline has been recognized. Crossplot analysis and petrophysical results indicate the heterogeneity of the field. Oil-water contact has been determined by the resistivity logs at -3052 ft SS (922.02 m)"--Abstract, page iii.